Closes issue 14636. mock objects raise exceptions from an iterable side_effect

Doc/library/unittest.mock-examples.rst

@@ -838,56 +838,6 @@ and the `return_value` will use your subclass automatically. That means all
 children of a `CopyingMock` will also have the type `CopyingMock`.
 
 
-Multiple calls with different effects
--------------------------------------
-
-Handling code that needs to behave differently on subsequent calls during the
-test can be tricky. For example you may have a function that needs to raise
-an exception the first time it is called but returns a response on the second
-call (testing retry behaviour).
-
-One approach is to use a :attr:`side_effect` function that replaces itself. The
-first time it is called the `side_effect` sets a new `side_effect` that will
-be used for the second call. It then raises an exception:
-
-    >>> def side_effect(*args):
-    ...   def second_call(*args):
-    ...     return 'response'
-    ...   mock.side_effect = second_call
-    ...   raise Exception('boom')
-    ...
-    >>> mock = Mock(side_effect=side_effect)
-    >>> mock('first')
-    Traceback (most recent call last):
-        ...
-    Exception: boom
-    >>> mock('second')
-    'response'
-    >>> mock.assert_called_with('second')
-
-Another perfectly valid way would be to pop return values from a list. If the
-return value is an exception, raise it instead of returning it:
-
-    >>> returns = [Exception('boom'), 'response']
-    >>> def side_effect(*args):
-    ...   result = returns.pop(0)
-    ...   if isinstance(result, Exception):
-    ...     raise result
-    ...   return result
-    ...
-    >>> mock = Mock(side_effect=side_effect)
-    >>> mock('first')
-    Traceback (most recent call last):
-        ...
-    Exception: boom
-    >>> mock('second')
-    'response'
-    >>> mock.assert_called_with('second')
-
-Which approach you prefer is a matter of taste. The first approach is actually
-a line shorter but maybe the second approach is more readable.
-
-
 Nesting Patches
 ---------------
 

Doc/library/unittest.mock.rst

@@ -823,6 +823,20 @@ a `StopIteration` is raised):
           ...
         StopIteration
 
+If any members of the iterable are exceptions they will be raised instead of
+returned::
+
+        >>> iterable = (33, ValueError, 66)
+        >>> m = MagicMock(side_effect=iterable)
+        >>> m()
+        33
+        >>> m()
+        Traceback (most recent call last):
+         ...
+        ValueError
+        >>> m()
+        66
+
 
 .. _deleting-attributes:
 

Lib/unittest/mock.py

@@ -891,7 +891,10 @@ class CallableMixin(Base):
                 raise effect
 
             if not _callable(effect):
-                return next(effect)
+                result = next(effect)
+                if _is_exception(result):
+                    raise result
+                return result
 
             ret_val = effect(*args, **kwargs)
             if ret_val is DEFAULT:
@@ -931,8 +934,9 @@ class Mock(CallableMixin, NonCallableMock):
       arguments as the mock, and unless it returns `DEFAULT`, the return
       value of this function is used as the return value.
 
-      Alternatively `side_effect` can be an exception class or instance. In
-      this case the exception will be raised when the mock is called.
+      If `side_effect` is an iterable then each call to the mock will return
+      the next value from the iterable. If any of the members of the iterable
+      are exceptions they will be raised instead of returned.
 
       If `side_effect` is an iterable then each call to the mock will return
       the next value from the iterable.

Lib/unittest/test/testmock/testmock.py

@@ -868,6 +868,16 @@ class MockTest(unittest.TestCase):
         self.assertRaises(StopIteration, mock)
 
 
+    def test_side_effect_iterator_exceptions(self):
+        for Klass in Mock, MagicMock:
+            iterable = (ValueError, 3, KeyError, 6)
+            m = Klass(side_effect=iterable)
+            self.assertRaises(ValueError, m)
+            self.assertEqual(m(), 3)
+            self.assertRaises(KeyError, m)
+            self.assertEqual(m(), 6)
+
+
     def test_side_effect_setting_iterator(self):
         mock = Mock()
         mock.side_effect = iter([1, 2, 3])